"Instructions posted by the moderators of the GunsForSale subreddit warn users to comply with federal and state laws, and many sellers on the site say that they transfer guns through FFLs, which conduct background checks on buyers. But some user comments suggest that sellers may be exploiting a loophole in federal law to traffic firearms—including talk of licensed dealers selling guns without conducting background checks, which in some circumstances would be illegal."

Other online gun marketplaces, such as Armslist.com, have been running into similar problems. The sites can attract people who want to exploit loopholes by selling their guns online as "private sellers" who aren't subject to the same regulations as gun dealers.

Mother Jones notes that even some licensed gun dealers on Reddit could be selling weapons without conducting background checks.

Thousands of guns are posted for sale on the GunsForSale subreddit and 159 transactions have been completed since June.

Reddit told Mother Jones that it neither condones nor doesn't condone the sale of guns on its site, but in 2011, the site authorized the use of its logo on assault rifles ordered by a Redditor.